A. Field of the Invention
The invention relates to devices and methods for repairing or maintaining the integrity of cardiac stimulator leads. In particular, the devices and methods disclosed as useful in the repair or maintenance of such leads are configured as sleeves which can be positioned over a section of lead in need of repair.
B. Description of the Related Art
Endocardial leads have become the standard for both pacing and cardioversion/defibrillation implantable cardiac stimulators. These leads typically exhibit a long implantation life. However, failures do occur. Brinker, "Endocardial Pacing Leads: The Good, the Bad, and the Ugly," PACE, Vol. 18, May 1995, Part I, Pg. 953 et seq.
Failure may result from a breach of lead integrity (insulation, wire stiffener, or conductor), or an uncoupling of the electrode-myocardial interface caused by tip displacement. In the pacemaker-dependent patient, lead failure can result in significant morbidity and even death.
Considerable attention has recently been directed to breaches in the integrity of polyurethane insulation used for pacing leads. The use of this material resulted in the development of smaller diameter leads than were previously possible with traditional silicone rubber materials. Unfortunately, certain lead models using Pellethane.TM. (Dow Chemical) 80A polyurethane exhibited failure resulting from degradation of the insulation due to environmental stress cracking and metal ion oxidation. Insulation failure may not be recognized until years after market release. In situs detection of insulation failure is difficult and requires careful monitoring. Parsonnet, "The Retention Wire Fix," PACE, Vol. 18, May 1995, Part I, Pg. 955 et seq.
In certain leads, a small (3.5 inches long, 0.013 inches wide, and 0.0065 inches thick) metal J-shaped retention ribbon located beneath the outer insulation may fracture and erode through the insulation. This protruding metal fragment may puncture the heart and has been associated with the death of patients and pericardial tamponade in others. Although these types of products have been recalled, some 40,000 leads had already been utilized worldwide, over half of which were implanted in the United States prior to 1994. Screening such leads by fluoroscopy has revealed signs of retention wire fracture in about 12% of patients. Lloyd, "Atrial `J` Pacing Lead Retention Wire Fracture: Radiographic Assessment, Incidence of Fracture, and Clinical Management, " PACE, Vol. 18, May 1995, Part I, Pg. 958 et seq.
Prior techniques and devices used with patients with lead failure usually involved implantation of a new lead, and optionally extracting the problem lead. While atrial lead malfunction rarely results in significant morbidity, the presence of a lead stiffener wire fracture represents a threat to the patient. Physicians have, in the past, been faced with a difficult choice: whether or not to remove a functioning lead with an inherent potential for serious morbidity, or risk lead extraction. Lead extraction may have a risk of serious complication of 2.5% and a mortality of 0.6%, while the risk of retaining the lead is unknown but presumably persists as long as the lead remains in situ. Smith et al., "Five-Years Experience With Intravascular Lead Extraction," PACE 1994; Vol. 17, Pt. II, Pg. 2016 et seq.
Where lead-related complications require lead removal (lead extraction), a number of techniques have been used. Initially, only patients with life-threatening complications such as septicemia were considered candidates for lead removal. The risk and morbidity of extracting the leads had to be weighted against the medical risk and morbidity of leaving them in place.
Extraction techniques have ranged from simple procedures requiring only a few minutes under local anesthesia to complicated procedures lasting hours under general anesthesia. Lead extraction is potentially dangerous. Complications include failure to extract an infected lead, low cardiac output, lead breakage and migration, avulsion of veins and myocardial tissue (e.g, muscle, tricuspid valve), and tears of the veins and heart wall with hemothorax, tamponade, and death.
All current lead extraction procedures use some form of traction. Counteraction is applied through the implant vein using an superior vena cava approach and indirectly through the femoral vein using an inferior vena cava approach. Pulling on the lead was a successful method of extracting the lead during the early years of pacing, when leads lacked efficient fixation devices and were implanted for short periods of time. Traction may be unsafe and have a high incidence of failure when applied to leads with efficient fixation devices and leads implanted for longer periods of time. Failure to extract a lead frequently damages the lead, making future extraction attempts more difficult.
While it is possible to introduce additional insulation or cladding throughout the length of the lead to prevent the threat of fracturing, this is not routinely done. Surgical practice indicates that thicker leads tend to be stiffer and more difficult to place in the restricted cavities and channels of the body. For this reason, the modern trend is to make such leads as thin as reasonably possible. This trend heightens the possibility of lead failure, breakage and shorting.
Devices are needed which can be positioned over lead sections which are known to be flawed or which are at risk of failure. Particularly, such lead repair devices are needed which can protect a patient with an implanted cardiac stimulator whose flawed lead represents a threat to health or life if left unrepaired. Preferably, such devices will be able to be positioned at various points along the length of a lead at the discretion of the heart surgeon. Such devices will be of particular usefulness if they can repair or protect a patient whose lead wire stiffener has fractured or where a defibrillation lead might unwind upon retraction, worsening prognosis for removal of the lead.